The present invention relates to height adjustable supports for office equipment and the like, and in particular to an adjustable height support that includes a counterbalance mechanism with a substantially constant counterbalance force.
Various types of desks and other supports have been used in office environments for office equipment, such as computers and the like. Worksurfaces may be used by different individuals for different types of tasks such that a fixed-height worksurface does not provide the desired degree of adjustability. Accordingly, adjustable height worksurfaces have been developed to provide flexibility for various applications and different user's requirements.
Some types of height adjustable worksurfaces include a manual, gear driven height adjustment arrangement that requires an operator to manually turn a crank handle for height adjustment. This type of an arrangement may require substantial physical exertion by the user. Also, because the crank handle must be turned a large number of revolutions to adjust the worksurface weight a substantial amount, this arrangement does not allow for quick adjustment of the worksurface height.
Other known height adjustable worksurfaces utilize a load compensator spring or counterbalance. This arrangement produces a lifting force biasing the worksurface into a raised position, with a releasable lock to hold the worksurface at a user-selected height. With a weight, such as a computer, resting on the worksurface, a user can release the stop, grasp the worksurface, and move the worksurface to the desired height. Ideally, the lifting force is about equal to the weight on the worksurface, such that the worksurface can be moved upwardly or downwardly without excessive effort by the user. Although some designs have an adjustable lifting force, because the user cannot easily determine what the magnitude of the lifting force is set at, it may be difficult for a user to properly adjust the lifting force to match the weight on the worksurface. If the lifting force is set improperly such that an imbalanced condition exists, excessive effort by the user may be required to move the worksurface to the desired height. In addition, if the lock is released when the worksurface is imbalanced, the worksurface may move suddenly upward or downward. Further, known height locks may not engage in a secure manner, such that the worksurface moves when additional weight is placed on the worksurface.
In addition, known load compensator spring or counterbalance devices do not normally provide a constant counterforce over the range of adjustment of the worksurface. One type of known compensator spring arrangement includes a tension spring with a flexible line connected to the spring at one end, and wrapped around a cam at the other. The cam surface is chosen to provide an approximately constant torque at a given spring preload. However, if the spring preload tension is changed to compensate for a greater or lesser weight resting on the worksurface, the lifting force will no longer be constant as the height of the worksurface is varied, but rather will increase or decrease as the worksurface is raised and lowered.